As the pupil of the eye, the hole or the opening of the uveous coat, or iris, through which the rays of light pass, and falling upon the retina, there depict every object in its natural colour, as upon a piece of white paper. Now the pupil of the eye being essentially necessary to sight, and easily injured, it is not only, in common with the other parts, deeply entrenched in the skull, ramparted with the forehead and cheek bones, defended by the eyebrows, eyelids, and eyelashes, and placed so as to be best protected by the hands, but, by a wonderful mechanism, is contracted or dilated by the muscular power of the iris, without which an excess of light would cause instant blindness.